U.S. patent number 6,031,827 [Application Number 08/802,645] was granted by the patent office on 2000-02-29 for method for radio resource control.
This patent grant is currently assigned to Nokia Mobile Phones Limited. Invention is credited to Kalle Ahmavaara, Kari Rikkinen, Mika Rinne, Mikko Rinne.
United States Patent |
6,031,827 |
Rikkinen , et al. |
February 29, 2000 |
Method for radio resource control
Abstract
In order to control the use of physical radio resources, the
physical radio resources are divided into chronologically
consecutive frames (14), so that a frame contains slots (16, 17,
18) of various sizes, which slots represent a given share of the
physical radio resources contained in the frame and can be
individually allocated to different radio connections. The first
dimension of a frame is time and the second dimension can be time,
frequency or code. In the direction of the second dimension the
slots represent various sizes, and a given first integral number of
slots of the first size can be modularly replaced by another
integral number of slots of another size. A certain number of
consecutive frames form a superframe (19), in which case frames
with corresponding locations in consecutive superframes are equal
in slot division and allocations, if the data transmission demands
do not change. Changes in the state of occupancy of the slots are
possible at each superframe. In order to form an uplink connection,
the mobile station sends a capacity request, where it indicates the
type of requested connection and the demand of resources. In order
to form a downlink connection, the base station subsystem sends a
paging call, where it indicates the location in the superframe of
the slots allocated to the connection. In order to indicate the
state of occupancy, the base station subsystem maintains a
superframe-size parametrized reservation table.
Inventors: |
Rikkinen; Kari (Oulu,
FI), Ahmavaara; Kalle (Helsinki, FI),
Rinne; Mikko (Helsinki, FI), Rinne; Mika (Espoo,
FI) |
Assignee: |
Nokia Mobile Phones Limited
(Salo, FI)
|
Family
ID: |
8546937 |
Appl.
No.: |
08/802,645 |
Filed: |
February 19, 1997 |
Foreign Application Priority Data
Current U.S.
Class: |
370/330; 370/335;
370/347; 370/468; 370/343 |
Current CPC
Class: |
H04B
7/2656 (20130101); H04W 72/0446 (20130101); H04W
28/06 (20130101); H04W 28/26 (20130101); H04W
48/08 (20130101); H04W 76/10 (20180201); H04W
74/04 (20130101); H04W 84/042 (20130101); H04W
68/00 (20130101) |
Current International
Class: |
H04Q
7/38 (20060101); H04B 7/26 (20060101); H04Q
007/00 (); H04B 007/216 (); H04J 001/00 (); H04J
003/16 () |
Field of
Search: |
;370/468,329,346,347,348,330,336,337,335,342,321,322 ;375/202 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0399611 A2 |
|
Nov 1990 |
|
EP |
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0615393 A1 |
|
Sep 1994 |
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EP |
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0633671 A2 |
|
Jan 1995 |
|
EP |
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0670640 A2 |
|
Sep 1995 |
|
EP |
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2174571 |
|
Nov 1986 |
|
GB |
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WO 95/12931 |
|
May 1995 |
|
WO |
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WO 96/10320 |
|
Apr 1996 |
|
WO |
|
Other References
Electronics Letters, vol. 32, No. 13, Jun. 20, 1996, pp. 1175,
1176, XP000599175, Ikeda T et al., "TDMA Based Adaptive Modulation
With Dynamic Channel Assignment (AMDCA) For Large Capacity Voice
Transmission in Microcellular Systems". .
European Search Report..
|
Primary Examiner: Olms; Douglas W.
Assistant Examiner: Vincent; David R
Attorney, Agent or Firm: Perman & Green, LLP
Claims
We claim:
1. A method for controlling physical radio resources in a radio
system comprising a base station subsystem and several mobile
stations in radio connection thereto, comprising the steps of:
dividing the physical radio resources into chronologically
consecutive frames, said frames containing two-dimensional integral
slots having varying data transmission capacities,
sizing each integral slot to represent a given share of the
physical resources contained in the frame, and
separately allocating each slot to the use of a given radio
connection.
2. A method according to claim 1, wherein the slots contained in
the frame belong, according to the volume of the respective
physical radio resources, to at least two different allowed size
categories, and that in order to change the slot structure of a
frame, a predetermined integral number of the slots of a first size
category can be replaced by a predetermined integral number of the
slots of a second size category.
3. A method according to claim 2, wherein the amount of allowed
size categories is three, with the slot of the largest size
category being equal to two slots of the next largest size category
or to ten slots of the smallest size category.
4. A method according to claim 2, wherein the amount of allowed
size categories is four, with the slot of the largest size category
being equal to two slots of the next largest size category, four
slots of the third largest size category or eight slots of the
smallest size category.
5. A method according to claim 1, wherein a first dimension of the
slots is time and a second dimension of the slots is one of the
following: time, frequency, code.
6. A method according to claim 5, wherein each frame is divided, in
the direction of a first dimension, into a predetermined amount of
time slots, and each time slot is further divided into slots.
7. A method according to claim 6, wherein time-time-division is
applied, such that each slot occupies the whole frequency range of
the corresponding time slot and the length of each slot in the time
dimension depends on its data transmission capacity.
8. A method according to claim 6, wherein time-frequency division
is applied, such that each slot occupies the whole chronological
duration of the corresponding time slot and the width of each slot
in the frequency dimension depends on its data transmission
capacity.
9. A method according to claim 6, wherein time-code division is
applied, such that each slot occupies the whole chronological
duration of the corresponding time slot and the data transmission
capacity of each slot depends on the corresponding spreading
code.
10. A method according to claim 1, wherein a predetermined
non-negative integral number of consecutive frames form a
superframe, and in consecutive superframes, the frames that are
located in similar positions when starting from the beginning of
the superframe correspond to each other with respect to the slot
division, if changes have not occurred in the data transmission
need of the radio connections in between the superframes.
11. A method according to claim 10, wherein each superframe
contains both slots meant for transmission of information and
control slots for realizing logic control channels.
12. A method according to claim 11, wherein a downlink signal
comprises a general logic control channel provided for the
signalling connected to slotwise radio resource control.
13. A method according to claim 11, wherein the slots contained in
the frame belong, according to the volume of the respective
physical radio resources, to at least two different allowed size
categories, and each control slot belongs, according to the
physical radio resources represented thereby, to one of the allowed
size categories.
14. A method according to claim 1, wherein a predetermined
frequency band is used to convey both downlink slots and uplink
slots according to a time-division duplexing scheme.
15. A method according to claim 14, wherein a predetermined
non-negative integral number of consecutive frames forms a
superframe and each superframe contains a first number of downlink
frames and a second number of uplink frames.
16. A method according to claim 14, wherein a predetermined first
frequency band is used to convey nominally downlink slots and a
predetermined second frequency band is used to convey nominally
uplink slots, and in response to unsymmetrical traffic conditions
in the uplink and downlink directions, slots are cross-allocated so
that nominally downlink slots are used to convey uplink traffic or
nominally uplink slots are used to convey downlink traffic.
17. A method according to claim 1, wherein the base station
subsystem maintains a reservation table in order to indicate the
size and state of occupancy of the slots in the frames and to
maintain an optimal rate of usage.
18. A method according to claim 17, wherein the base station
subsystem makes a decision of allocating the slots for the radio
connections on the basis of
the data transmission needs of the radio connections,
the changes in the data transmission needs of the radio
connections, and
the size and state of occupancy of the slots indicated by the
reservation table.
19. A method according to claim 18, wherein the base station
subsystem evaluates the quality of at least one allocatable slot
and makes a decision of allocating or non-allocating said slot to a
connection on the basis of the transmission quality required by
said connection.
20. A method according to claim 18, wherein the base station
subsystem performs the steps in which, as a response to a slot
request,
either uplink or downlink frame storage is chosen,
a frame storage is chosen,
a set of candidate time slots from the chosen frame storage is
formed,
a set of predetermined selection criteria is applied to find the
best candidate time slot,
the transmission quality offered by the selected best candidate
time slot is checked, and
a decision to allocate a slot from the best candidate time slot is
made.
21. A method according to claim 18, wherein the base station
subsystem makes a decision of allocating the slots for the radio
connections also on the basis of the information contained in the
reservation tables of neighbouring base station subsystems.
22. A method according to claim 21, wherein the base station
subsystem allocates slots on the basis of the transmission power
used for communication by different mobile stations, and a first
mobile station that uses low transmission power to communicate with
a first base station is allocated a slot that coincides
chronologically with a slot allocated to a second mobile station
that uses high transmission power to communicate with a second base
station.
23. A method according to claim 21, wherein the base station
subsystem allocates slots on the basis of the communication type
used by different mobile stations, and circuit-switched and
packet-switched connections have their own slots located in the
reservation tables of adjacent base stations in optimal locations
with respect to the total interference of the system.
24. A method for setting up an uplink radio connection between a
base station subsystem and a mobile station in a radio system
comprising a base station subsystem and several mobile stations, in
which radio system the physical radio resources are divided into
chronologically consecutive frames, wherein the method comprises
the steps of:
dividing said frames into two-dimensional integral slots having
varying data transmission capacities,
transmitting from the mobile station, in an allowed uplink capacity
request slot, a capacity request (21, 35), where the mobile station
indicates the amount of physical radio resources required by the
uplink radio connection, and
making an allocation decision in the base station subsystem as to
the data transmission capacities of said two-dimensional integral
slots in response to said capacity request.
25. A method according to claim 24, wherein the location and amount
of the allowed uplink capacity request slots in relation to the
frame structure is not constant and the base station subsystem
transmits, in a predetermined downlink slot, an announcement
indicating the location and amount of the allowed uplink capacity
request slots.
26. A method according to claim 24, wherein the radio system
additionally offers the mobile station realtime and non-realtime
data transmission services, and in order to reserve radio resources
for the use of a radio connection for uplink realtime data
transmission services, the mobile station indicates in its capacity
request
the required data transmission capacity in the form of at least one
slot size, and
a predetermined set of parameters describing the required qualities
of the radio connection.
27. A method according to claim 26, wherein when the data
transmission capacity demand grows during an ongoing radio
connection for uplink realtime data transmission services, the
mobile station sends the base station subsystem a capacity request
indicating the required additional data transmission capacity in
the form of at least one slot size.
28. A method according to claim 26, wherein when the data
transmission capacity demand diminishes during an ongoing radio
connection for uplink realtime data transmission services having
several allocated slots, the mobile station leaves at least one of
the allocated slots unused.
29. A method according to claim 26, wherein each mobile station has
a certain temporary logic identifier in order to distinguish the
mobile station from other mobile stations operating under the same
base station subsystem, and in order to reserve radio resources for
the use of a radio connection for parallel uplink realtime data
transmission services, the mobile station sends the base station
subsystem a capacity request comprising:
a temporary logic identifier for said mobile station,
the required parallel data transmission capacity in the form of at
least one slot size,
a predetermined set of parameters describing the required qualities
of the parallel radio connection, and
an additional identifier, which distinguishes the parallel radio
connection from other ongoing radio connections conveying realtime
data transmission services.
30. A method according to claim 24, wherein the radio system
additionally offers the mobile station realtime and non-realtime
data transmission services, and in order to reserve radio resources
for the use of a radio connection for uplink non-realtime data
transmission services, the mobile station indicates in its capacity
request:
the amount of data to be transmitted, and
a predetermined set of parameters describing the required qualities
of the radio connection.
31. A method according to claim 24, wherein in its allocation
decision the base station subsystem has the freedom of directing
the required radio connection into any available slot and after the
allocation decision the base station subsystem transmits to the
mobile station in a predetermined downlink access granting slot an
indication of the granted slot or slots.
32. A method for setting up a downlink radio connection between a
base station subsystem and a mobile station in a radio system
comprising a base station subsystem and several mobile stations, in
which radio system the physical radio resources are divided into
chronologically consecutive frames, said method comprising the
steps of:
dividing said frames into two-dimensional integral slots having
varying data transmission capacities,
making an allocation decision in the base station subsystem as a
response to the detected need of a new downlink radio connection
indicating the amount of physical radio resources required by the
new downlink radio connection,
transmitting from the base station subsystem to the mobile station
a paging message, that announces the location of the downlink slot
or slots allocated to the new downlink radio connection in said
allocation decision,
as a response to a detected paging message, transmitting from the
mobile station a paging acknowledgement message, and
as a response to a detected paging acknowledgement message,
commencing downlink transmission from the base station
subsystem.
33. A method according to claim 32, wherein the radio system
additionally offers the mobile station realtime and non-realtime
data transmission services, and in order to form a radio connection
for downlink realtime data transmission services, the base station
subsystem indicates in the paging message, for the regularly
repeated slots allocated to the radio connection, their location in
relation to the frame structure.
34. A method according to claim 33, wherein when the data
transmission capacity demand grows during an ongoing radio
connection for downlink realtime data transmission services, the
base station subsystem makes an additional slot allocation decision
and sends the mobile station a paging message, that announces the
location of the additional downlink slot or slots allocated to the
radio connection.
35. A method according to claim 33, wherein when the data
transmission capacity demand diminishes during an ongoing radio
connection for downlink realtime data transmission services having
several allocated slots, the base station makes a slot deallocation
decision concerning at least one of the allocated slots and leaves
the corresponding slots unused.
36. A method according to claim 33, wherein each mobile station has
a given temporary logic identifier in order to distinguish the
mobile station from other mobile stations operating under the same
base station subsystem, and in order to reserve radio resources for
the use of a radio connection for parallel downlink realtime data
transmission services, the base station subsystem sends the mobile
station a paging message indicating:
the temporary logic identifier of the mobile station,
the location of the regularly repeated slots allocated to the
parallel radio connection, and
an additional identifier, which distinguishes the parallel radio
connection from other ongoing radio connections conveying realtime
data transmission services.
37. A method according to claim 32, wherein the radio system
additionally offers the mobile station realtime and non-realtime
data transmission services, and in order to form a radio connection
for downlink non-realtime data transmission services, the base
station subsystem indicates in the paging message the location of
the first slots for non-realtime data transmission services in
relation to the frame structure, and to announce a change in either
the location or the amount of the slots allocated for non-realtime
data transmission services during the connection, the base station
subsystem notifies of the new location or amount of the slots by
sending a new paging message.
38. A base station subsystem for a radio telecommunication system
having base station subsystems and mobile stations which
respectively communicate information over radio connections, said
base station subsystem comprising:
means for arranging the communicated information into
chronologically consecutive frames, and
means for directing the communicated information of each radio
connection into at least one cyclically repeated two-dimensional
integral slot in the frames, the size of said one slot in relation
to the size of a frame being dependent on the data transmission
capacity required by the respective radio connection.
39. A base station subsystem according to claim 38, further
comprising means for maintaining a reservation table in order to
indicate the size and state of occupancy of the slots in the frames
and maintain an optimal rate of usage.
40. A base station subsystem according to claim 39, further
comprising means for communicating information concerning
reservation tables with its neighbouring base station
subsystems.
41. A base station subsystem according to claim 38, further
comprising means for setting up uplink connections comprising:
means for producing a general access slot location announcement and
transmitting it to all of the telecommunication system's mobile
stations in a predetermined downlink slot in order to advise the
mobile stations to send capacity requests in the announced access
slot,
means for receiving and interpreting capacity requests from the
mobile stations,
means for making slot allocation decisions that allocate slots to
radio connections requested and identified in the capacity
requests, and
means for producing access granting messages and transmitting them
in a predetermined slot selectively to those mobile stations the
capacity requests of which were granted in the slot allocation
decisions.
42. A base station subsystem according to claim 38, further
comprising means for setting up downlink connections
comprising:
means for producing paging messages and transmitting them in a
predetermined slot selectively to those mobile stations to which a
downlink connection is to be established, said paging messages
indicating at least one allocated downlink slot,
means for receiving and interpreting paging acknowledgement
messages from the mobile stations, and
means for directing a downlink transmission into the allocated
downlink slots indicated in the paging messages.
43. A mobile station for a radio telecommunication system having
base station subsystems and mobile stations, which respectively
communicate information over radio connections, said mobile station
comprising:
means for arranging the communicated information into
chronologically consecutive frames, and
means for directing the communicated information of each radio
connection into at least one cyclically repeated two-dimensional
integral slot in the frames, the size of said integral slot in
relation to the size of a frame being dependent on the data
transmission capacity required by the respective radio
connection.
44. A mobile station according to claim 43, further comprising
means for setting up uplink connections comprising:
means for receiving and interpreting access slot location
announcements transmitted from a base station subsystem,
means for producing a capacity request and transmitting it in an
access slot identified in an access slot location announcement,
means for receiving and interpreting an access grant message from
the base station subsystem identifying at least one granted slot,
and
means for directing information transmissions into said at least
one identified granted slot.
45. A mobile station according to claim 43, further comprising
means for setting up downlink connections comprising:
means for receiving and interpreting paging messages transmitted
from a base station subsystem, said paging messages indicating at
least one allocated downlink slot and at least one acknowledgement
slot,
means for producing a paging acknowledgement message and
transmitting it in an acknowledgement slot identified in an access
slot location announcement, and
means for receiving and interpreting downlink transmissions in said
at least one allocated downlink slot.
46. A radio telecommunication system having base station subsystems
and mobile stations, which respectively communicate information
over radio connections and comprise:
means for arranging the communicated information into
chronologically consecutive frames, and
means for directing the communicated information of each radio
connection into at least one cyclically repeated two-dimensional
integral slot in the frames, the size of said integral slot in
relation to the size of a frame being dependent on the data
transmission capacity required by the respective radio connection.
Description
TECHNOLOGICAL FIELD
The invention relates generally to sharing radio resources between
various users in a cellular radio system. Particularly the
invention relates to sharing radio resources in a system where the
users'data transmission needs, both in quality and quantity, change
rapidly.
BACKGROUND OF THE INVENTION
At the moment of filing this application, the most general form of
mobile personal telecommuication is a second-generation digital
cellular radio network; these networks include the European systems
GSM (Global system for Mobile telecommunications) and its extension
DCS1800 (Digital Communications System at 1800 MHz), the North
American (USA) systems IS-136 (Interim Standard 136), IS-95
(Interim Standard 95) and the Japanese system PDC (Personal Digital
Cellular). These systems transmit mainly speech, telefaxes and
short text messages, as well as digital data at a limited speed,
for instance files transmitted between computers. Several
third-generation systems are being designed, the aims being
world-wide coverage, a large selection of data transmission
services and a flexible sharing of capacity, so that a given user
may, when desired, transmit and/or receive even a large amount of
data at a high speed.
The European Telecommunications Standards Institute ETSI has
suggested a third-generation mobile telecommunications system
called UMTS (Universal Mobile Telecommunications System). Its aim
is a wide operating environment including homes, offices, urban and
rural environments as well as stationary and mobile stations. The
selection of services is large, and in addition to the currently
known mobile telephones, the types of mobile stations include for
instance multimedia terminals and multipurpose terminals that
mediate telecommunications between the UMTS system and various
local systems.
FIG. 1 illustrates an exemplary cell 11 of the UMTS system,
provided with a stationary base station subsystem 12 (BSS), within
the range of which there exist or move, along with the users,
several different mobile stations 13. The base station subsystem
may comprise one or several base stations, as well as a base
station controller controlling their operation. In between the base
station subsystem and the mobile stations, there is a radio
connection, for which a given radio frequency range is reserved,
and the operation of which is regulated by the specifications of
the system. The time and frequency range available for the radio
connection together define so-called physical radio resources. One
of the biggest challenges of the base station subsystem is to
control the use of these physical radio resources so that all
terminals located in the cell coverage are at any moment capable of
receiving data transmission services of the requested quality, and
that adjacent cells interfere with each other as little as
possible.
From the prior art systems, there are known several methods for
sharing radio resources. In time division multiple access (TDMA),
each of the employed transmission and reception frequency bands is
divided into time slots, among which the base station subsystem
allocates one or several cyclically repeated time slots to the use
of a given terminal. In frequency division multiple access (FDMA),
the utilised frequency range is divided into very narrow bands,
among which the base station subsystem allocates one or several to
each terminal. Many current systems apply a combination of these,
where each narrow frequency band is further divided into time
slots. In coded division multiple access (CDMA), each connection
between the mobile station and the base station subsystemobtains a
spreading code, whereby the transmitted information is spread
randomly within a fairly large frequency range. The codes used
within the cell coverage are mutually orthogonal or nearly
orthogonal, in which case a receiver that recognises the code may
distinguish the desired signal and attenuate other simultaneous
signals. In orthogonal frequency division multiplex (OFDM), suited
mainly for broadcasting-type services, data is transmitted from the
transmitting central station on a wide frequency band, which is
divided into equidistant sub-frequencies, and the simultaneous
phase shifts of these sub-frequencies create a two dimensional bit
flow in the time-frequency space.
As for the technology of packet switched radio networks, there are
also known various packet-based connection protocols, where the
connection between the mobile station and the base station
subsystemis not continuous but proceeds in packages with pauses of
varying durations in between. Compared with continuous connection
Systems, i.e. with so-called circuit-switched networks, there is
achieved the advantage that the radio resources required by a given
connection are not unnecessarily occupied when there is a temporary
pause in the connection. A drawback is generally a longer data
transmission delay, because after each pause, the transmission of a
new packet requires the exchange of certain control or signalling
messages between the mobile station and the base station. Delays
can also be caused by different routing of the packages between
transmitter and receiver.
It is typical of third-generation cellular radio networks that for
instance in the case of FIG. 1, with some of the terminals 13 it
suffices to have a fairly low-capacity radio connection with the
base station, but some of them need, at least temporarily, a
remarkably larger share of the common radio resources than the
others. Low-capacity connections can be for example speech
connections, and a high-capacity connection can be for example the
loading of an image file in a data network connection via the base
station subsystemto the mobile station, or a video image connection
during a videophone call. In the prior art, there is not known a
method where the base station subsystem could divide the available
radio resources in a flexible and dynamic way between the various
users.
OBJECT OF THE INVENTION
An object of the present invention is to introduce a method for a
flexible and dynamic division of radio resources in the base
station subsystem of a cellular radio network.
SUMMARY OF THE INVENTION
The object of the invention is achieved by dividing the radio
resources in the base station subsystem--or in a similar
arrangement responsible for the division of radio resources--into
frames, among which the base station subsystem can allocate,
according to the traffic demands of the moment, various sizes of
modular, parametrized sections to be used by the different
connections. These frames are repeated cyclically so that the
repetition sequence contains either a single frame or a group of
consecutive frames.
The method of the invention is characterised in that the physical
radio resources are chronologically divided into consecutive frames
that contain slots with varying data transmission capacities, so
that each slot represents a given proportion of the physical
resources contained in the frame, and each slot can be separately
allocated to the use of a given radio connection.
In the method of the invention, the so-called physical layer of the
transmission channel between a first radio station and a second
radio station is divided into frames. The exemplary denominations
"base station" and "mobile station" are used to distinguish the
radio stations from each other throughout this patent application.
Each frame may be further divided into smaller units, the size of
which is defined by two coordinates or dimensions, which makes the
subdivision of a frame conceptually two-dimensional in structure.
The first dimension is time; this means that the frame has a given
duration in time, which can be further divided into consecutive
time slots. In a preferred embodiment of the invention, each frame
contains an equal number of time slots, but the usage of the time
slots may vary from one frame to another. The second dimension can
be time, frequency or code. If also the second dimension is time,
each time slot of the frame is further divided into smaller
sub-time slots. If the second dimension is frequency, there can be
extracted, in each time slot contained by the frame, frequency
bands that are narrower than the total allocated frequency band
covered by the frame. If the third dimension is code, a given
number of mutually orthogonal or nearly orthogonal codes is
available during each time slot.
The smallest resource unit to be allocated from one frame is a
slot, the size of which is in the first dimension defined by the
length of the time slot and in the second dimension by a division
unit determined according to the nature of the second dimension.
For instance in a time-frequency frame, the size of the slot in the
second dimension is the bandwidth of the frequency band employed in
each case. One slot is always allocated as a whole to the use of
one connection. It is important to notice that in this patent
application, a time slot is conceptually a different thing than a
slot. A time slot is generally a division unit of a frame in the
time dimension. A slot is the unit of physical radio resources that
may be allocated to a single connection.
A certain predetermined number of consecutive frames forms the
so-called superframe. Because in digital systems various numbers in
general are most naturally powers of two, the superframe
advantageously contains 1, 2, 4, 8, 16, 32 or 64 frames. The
flexibility and dynamic adaptability of the method according to the
invention are both due the fact that the slots contained by a given
frame are not necessary equal in size, that the slot structure of
the frames contained in the superframe is not necessarily similar,
and that it is not necessary to allocate an equal number of slots
from a frame or superframe to each connection. The slot structure
and the reservation of slots for the use of various connections can
change superframe by superframe. On the other hand, if the data
transmission need does not change, the first frame in a given
superframe has a similar slot structure as the first frame of the
preceding superframe, the second frame is similar to the second
frame of the preceding superframe, and so forth. The word
superframe is naturally only an exemplary denomination to a concept
that may represent one or more consecutive frames.
In an uplink data transmission, i.e transmission that proceeds from
the mobile stations to the base station subsystem, the mobile
stations need some kind of arrangement by which they can reserve
data transmission capacity for use. In a preferred embodiment of
the invention, each uplink superframe contains random access slots,
during which the mobile stations can freely send packet-shaped
capacity requests. Respectively, downlink superframes contain
allocation grant slots, where the base station subsystem notifies
the granted allocations. Granting takes place on the basis of
capacity requests received successfully by the base station
subsystem and according to the priority regulations set for
different types of connections and the prevailing traffic load. The
base station subsystem advantageously maintains a superframe-size
reservation table, where it manages the allocations so that the
available radio resources are utilised in an optimal fashion.
In a downlink data transmission the base station subsystem
allocates data transmission capacity similarly according to the
priority regulations set for different types of connections and the
prevailing traffic load. It notifies the downlink allocations
preferably in the same paging messages that it uses to inform the
mobile stations about incoming downlink transmission requests. Once
a mobile station has acknowledged the correct reception of a paging
message, the downlink transmission may begin using the allocated
transmission capacity.
BRIEF DESCRIPTION OF DRAWINGS
The invention is described in more detail below, with reference to
the preferred embodiments presented as examples and to the appended
drawings, where
FIG. 1 illustrates a known cell in a cellular system,
FIG. 2a illustrates some structural elements of a frame according
to the invention,
FIG. 2b illustrates a variation of FIG. 2b,
FIG. 3 illustrates a superframe according to a preferred embodiment
of the invention,
FIG. 4a illustrates an uplink realtime data transmission according
to a preferred embodiment of the invention,
FIG. 4b illustrates a timing aspect of the messages of FIG. 4a,
FIG. 5a illustrates a downlink realtime data transmission according
to a preferred embodiment of the invention,
FIG. 5b illustrates a timing aspect of the messages of FIG. 5a,
FIG. 6a illustrates an uplink non-realtime data transmission
according to a preferred embodiment of the invention,
FIG. 6b illustrates a timing aspect of the messages of FIG. 6a,
FIG. 7a illustrates a downlink non-realtime data transmission
according to a preferred embodiment of the invention, and
FIG. 7b illustrates a timing aspect of the messages of FIG. 7a,
FIG. 8 illustrates a timing aspect of messages in asymmetric
transmission resource sharing according to a preferred embodiment
of the invention.
FIG. 9 illustrates full TDD operation according to the
invention,
FIG. 10 illustrates a method according to the invention for
regulating the transmission power, and
FIG. 11 illustrates an advantageous algorithm for slot
allocation.
FIG. 1 was already referred to above, in the description of the
prior art; therefore we shall mainly refer to FIGS. 2a-11 in the
description of the invention and its preferred embodiments below.
Like numbers for like parts are used in the drawings.
DISCUSSION OF PREFERRED EMBODIMENTS
FIG. 2a illustrates a two-dimensional frame 14 according to a
preferred embodiment of the invention. In the above description it
was maintained that the first dimension of the frame is time and
the second dimension can be either time, frequency or code. In the
case of FIG. 2a, the second dimension of the frame 14 is frequency
or time. The size of the frame in the direction of both dimensions
must be chosen so that it is compatible with other specifications
set for the system. In this example, the length of the frame in the
time direction is about 4.615 milliseconds, and it is divided, in
the time direction, into eight time slots, in which case the length
of one time slot 15 is about 0.577 ms. The frame width in the
frequency direction is about 2 MHz.
The smallest uniform structural elements of the frame, i.e. the
slots, are various subdivisions of a time slot 15. In the lower
left portion of FIG. 2a, time-frequency division is applied,
whereby the chronological length of each slot is the same as that
of a time slot, but its width in the frequency direction may be 200
kHz, 1 MHz or 2 MHz. Reference number 16 denotes a large, 0.577
ms.times.2 MHz slot, reference number 17 denotes a medium-sized,
0.577 ms.times.1 MHz slot, and reference number 18 denotes a small,
0.577 ms.times.200 kHz slot. In the lower right portion of the
Figure, time-time division is applied, whereby each slot employs
the whole 2 MHz bandwidth of the system but its chronological
duration may be 1/1, 1/2, or 1/10 of the length of a time slot.
Reference number 16 denotes again a large, 0.577 ms.times.2 MHz
slot, reference number 17 denotes a medium-sized, 0.2885 ms.times.2
MHz slot and reference number 18 denotes a small, 0.0577 ms.times.2
MHz slot. In those divisions in which five small slots share a time
slot with one medium-sized slot (row C: of the division examples),
it is naturally possible to present a mirror image alternative (for
example a time slot which begins with a medium-sized slot and ends
with five small slots).
According to another suggestion, the number of different slot size
categories is four, and their relative sizes are such that the slot
of the largest size category would correspond to two slots of the
second largest size category, four slots of the third largest size
category and eight slots of the smallest size category. Also other
arrangements for the relative slot sizes are possible.
A carrier wave solution, where one frame can contain several
elements with different widths on the frequency band, is called a
parallel multicarrier structure. The base station subsystem may
change the frame structure, so that it replaces one large slot by
two medium-sized, ten small or one medium-sized plus five small
slots or vice versa, or so that it replaces one medium-sized slot
by five small slots or vice versa. This property is called the
modularity of the frame: a given slot or slot group forms a module
(like the group of five small slots 18 on row C: of the division
examples), which can in the corresponding time slot contained in
some later frame be replaced by a different module (like a single
medium-sized slot 17 on row B: of the division examples), so that
the rest of the contents of the frame are not changed, and the
available bandwidth is always optimally utilised. The invention
does not as such limit neither the number of time slots contained
in the frame nor the widths of allowed carrier bands, but in order
to maintain modularity, it is particularly advantageous that the
slots are each other's integral multiples with respect to their
dimensions. For instance three 250 kHz wide slots in time-frequency
division could not be modularly replaced by 450 kHz wide slots, but
only one 450 kHz slot would fit in the space left by the three
narrower slots, and 300 kHz of the bandwidth would remain
unused.
The invention does not require that the frame would occupy a
continuous range of frequencies (2 MHz in FIG. 2a). It is possible
to define a frame so that it covers two or more separate frequency
bands. Even a single slot may cover two or more separate frequency
bands, which naturally requires the corresponding transceiver to
have multiple operation capabilities, i.e. in reception the
capability of receiving on at least two different reception
frequency bands simultaneously and combining the received
information correctly, and in transmission the capability of
dividing information into at least two separate transmitter
branches and transmitting it simultaneously on at least two
different transmission frequency bands.
FIG. 2b illustrates a CDMA alternative to the division of time
slots according to FIG. 2a. During each time slot 15 there may be a
different number of allowed spreading codes, with different
spreading ratios. The spreading ratio is a characteristic feature
of a spreading code and from the viewpoint of resource sharing it
defines how much physical radio resources must be allocated to a
single connection. The bigger the spreading ratio of a spreading
code used in a connection, the lower the bit rate in that
connection, and correspondingly the larger the number of possible
simultaneous connections during a given period of time using a
given bandwidth. In the example of FIG. 2b, three types of
spreading codes are available. The Code 1 type spreading codes have
such a small spreading ratio R that information that is transmitted
with a Code 1 type spreading code fills the capacity of a whole
time slot (row A:). The spreading ratio of Code 2 type spreading
codes is 2*R (i.e. twice that of Code 1), so two connections using
orthogonal or nearly orthogonal Code 2 type spreading codes may
exist simultaneously in a single time slot (row B). The Code 3 type
spreading codes have a spreading ratio 10*R (i.e. ten times that of
Code 1), so different combinations of orthogonal or nearly
orthogonal spreading codes may exist simultaneously; on row C. the
time slot accommodates five connections with Code 3 type spreading
codes and one with a Code 2 type spreading code, and on row D:
there are ten simultaneous connections with Code 3 type spreading
codes. A simple comparison between FIGS. 2a and 2b shows that the
time-code division may be interpreted to define slots in a fashion
that is analogous to the use of time-frequency or
time-time-division.
Apart from the slot dimensions, the capacity of a slot, i.e. the
amount of data that can be transmitted in one slot, depends on the
modulation and error protection methods used in the coding of the
data, as well as of the rest of the signal structure in the slot.
In the time-frequency arrangement according to FIG. 2a, where the
allowed bandwidths are 200 kHz, 1 MHz and 2 MHz, it has been found
advantageous to use, on the two narrower bandwidths (200 kHz and 1
MHz) a binary-offset QAM (B-O-QAM, Binary Offset Quadrature
Amplitude Modulation) and on the widest bandwidth (2 MHz) a
quaternary offset QAM (Q-O-QAM, Quaternary Offset Quadrature
Amplitude Modulation). Other modulation methods are also possible;
they are as such known to the person skilled in the art.
FIG. 3 illustrates a superframe according to a preferred embodiment
of the invention. It was already pointed out that the invention
does not limit the number of consecutive frames contained in the
superframe, but advantageous numbers are powers of two. At its
shortest, a superframe may consist of only one frame. In the case
of FIG. 3, the superframe 19 contains four chronologically
consecutive frames 14. Here the frames have consecutive numbers, so
that the number of the first frame is described by letter N
representing a non-negative integral, the next frame is N+1, the
next N+2 and the number of the last frame in the superframe is N+3.
The time slots of the frames are also numbered with consecutive
non-negative integrals, so that the first time slot in each frame
is number 0, and the last time slot is number 7. The drawing also
illustrates, by way of example, the division of the slots into
payload slots and control data slots. Slots containing payload
information, i.e. transmittable data proper, are marked with letter
I (Information), and the slots containing control data, i.e.
signalling data, are marked with letter C (Control).
The control data slots form one or several logic control channels,
which are available for instance for transmitting messages
controlling the starting, maintaining or ending of a connection,
for defining the need to change base stations and for exchanging
commands and measurements relating to the transmission power and
the power-saving mode of the mobile stations between the base
station subsystemand the mobile stations. It is advantageous to
place the control slots in a certain relatively compact portion of
each frame which contains control slots, because this way the rest
of the frame may be very flexibly allocated in different modular
slot combinations. If the control slots would be scattered all over
the frame structure, only a limited selection of allocatable slots
would fit between them.
According to the preferred embodiment of the invention, the base
station subsystem (or a corresponding arrangement responsible for
the division of radio resources) maintains a parametrized
reservation table, which indicates the size and state of occupancy
of each slot, as well as other possible parameters concerning the
slot. Changes in the slot structure of the frames 14 and/or in the
allocation of slots for the use of given connections take place in
between the superframes, i.e. the reservation table remains valid
for the duration of one superframe at a time. In order to ensure an
optimal operation, the base station subsystem must have a
reservation table routine, which maintains the reservation table
according to given evaluation criteria. Among such important
criteria that the reservation table routine takes into
consideration before granting access to a new connection are for
instance the traffic load, the type of information contained in the
new connection (for example speech, video, data), the priority
defined on the basis of the new connection (for example ordinary
call, emergency call), the general power level of the traffic load
as well as the type of the data transmission connection (for
example realtime, non-realtime). Moreover, it is possible to define
more sophisticated criteria, such as the susceptibility to
interference of a given slot, and the transmission power required
by the slot.
If a certain base station takes into consideration the reservation
tables of the surrounding base stations, too, it may in its own
reservation table allocate the slots according to the power level
and switching type of the connection. The former means that mobile
stations applying a high power level and a low power level have
their own allocated slots, which are located in the reservation
tables of adjacent base stations, in optimal locations with respect
to the total interference of the system. The latter means that
circuit-switched and packet-switched connections have their own
slots located in the reservation tables of adjacent base stations
in optimal locations with respect to the total interference of the
system. Optimality is defined so that all users suffer as little as
possible from the noise signals of other users. If the slots are
allocated for instance according to the power level, the first base
station grants low-power users (those located near the first base
station) such slots, during which in the second base station there
is a connection of a high-power user (one located far from the
second base station).
Previously known slot allocation methods are usually sequential (of
8 available slots, for example slot number 0 is allocated first,
then slot 1 and so on; or slot number 0 is allocated first, then
slots 2, 4, and 6 in this order, then slots 1, 3, 5, and 7) or
random. In connection with the present invention it has been found
advantageous to use a slot allocation method that takes into
consideration the different evaluation parameters that may be
presented to describe each slot. The base station subsystem may
measure the level of noise in each slot and arrange the free and
allocatable slots according to their quality, i.e. noise level. If
a new slot request indicates that the desired new connection should
have very tight realtime requirements with only limited
retransmission possibilities, the base station subsystem will give
it a very high-quality slot with low noise levels. A non-realtime
connection with good retransmission tolerance could get a
lower-quality slot, in order to keep the best slots free for
possible future realtime connection requests. The size of a slot is
important: if there are both small and large slots free and
available in a frame, and a new slot request indicates only a small
need of resources, it is advisable to allocate an existing small
slot for it even if it could getter a better quality slot through
replacement of a larger slot with a group of smaller slots in a
modular fashion and allocation of one of those.
The representation of the slot allocation method in the base
station subsystem may be an allocation equation or a logical
algorithm (conclusion chain). The former means that the base
station gives different calculational weights to the relevant
factors in consideration (noise level, realtime service
requirements, need for splitting of large slots, estimated power
level, etc.) and calculates a result that points at a certain slot.
The latter means that the base station subsystem maintains a set of
candidate slots and evaluates them one at a time to find out which
one would suit best to the newly requested connection.
FIG. 11 illustrates an exemplary logical algorithm that the base
station subsystem may use to determine, which slot it will allocate
to a given new connection. Operation begins with a slot request 100
which may come either from the network side (downlink slot request)
or from the mobile station's side (uplink slot request). In block
101 the base station subsystem checks, which frame storage (uplink
or downlink) it should choose. The actual selection of a storage
(reservation table) is done as a background process in blocks 102,
103, and 104, and the algorithm proceeds to block 106. Here a frame
selection process 107, 108, 109 similar to the frame storage
selection is initiated. In the Figure we suppose that each
superframe consists of two frames.
In block 110 the base station subsystem starts the evaluation
process from the time slot that has the lowest fragmentation value,
i.e. that contains the largest slots. In block 111 it rejects all
timeslots where the new connection would result in multicarrier
allocation. In block 112 it checks, whether there are any other
factors that would prevent the use of the time slot (too small slot
capacity, preset transmission power limitations, unacceptably high
noise levels etc.) and if not, it updates the set of candidate time
slots. Block 114 causes a repetition of steps 110, 111, 112, 113,
and potentially 105 until all timeslots have been scanned. In block
115 the base station finds the best candidate time slot by applying
certain radio resource management rules and selection criteria.
There may be for example two best candidates with equally low
interference, and the base station subsystem must examine, whether
the estimated power requirement for the new connection agrees with
certain preset power and noise limitations in each slot and whether
choosing of any of the best candidates would imply calculational
penalty in the form or splitting a large slot into smaller
ones.
After having made the selection in block 115, the base station
subsystem additionally checks in block 116, whether the calculated
quality estimates 117 indicate a sufficiently high transmission
quality. Normally the procedure continues to block 118, but it may
happen that even the best candidate slot will not offer enough
quality. In such cases the base station subsystem branches into
block 119, where it initiates a possible operation mode change to
enhance the transmission quality. The procedure ends in a slot
assignment decision 120.
In the method according to the invention, the sharing of radio
resources takes place in similar fashion both as regards realtime
and non-realtime services: the base station subsystem (or a
corresponding arrangement responsible for the division of radio
resources) allocates slots for each service according to their
needs. Similar control messages and mechanisms regulate the
distribution of radio resources in both cases; only the detailed
content of the control messages and some principles of allocation
and deallocation are somewhat different depending on the type of
service in question. Data transmission over radio path during an
already created connection is somewhat different depending on
whether the service in question is realtime or non-realtime.
Applications requiring realtime or nearly realtime service are for
instance speech transmission in packets and the video connection
required by a videophone. In a simulation of the method according
to the invention it was presupposed that in the transmission of
speech, in between the base station subsystem and the mobile
station there is achieved a bit error ratio (BER) 10.sup.-3, when
the longest allowed data transmission delay is 30 Ms. In a video
connection required by a videophone, the corresponding values are
10.sup.-6 and 100 ms, where the longer delay is caused by the time
interleaving of the transmitted data. These services apply a
forward error correction (FEC) type error correction and a radio
resource reservation protocol to be explained in more detail below.
A non-realtime service is for instance file transmission in an
ordinary Internet connection. It applies packet-type data
transmission and an ARQ-type error correction protocol (automatic
repeat on request).
We shall next observe realtime uplink data transmission in an
ordinary case, with reference to FIGS. 4a and 4b. The arrows of the
FIG. 4a represent data transmission between a base station (BS) and
a mobile station (MS) in chronological order so that time in the
drawing passes from top to bottom. Certain superframes transmitted
by the base station contain so-called Y slots, where the base
station notifies when in the uplink direction there are next found
PRA (packet random access) slots, i.e. such points in the uplink
superframe where the mobile stations can send capacity requests.
Arrow 20 represents the data transmitted in an Y slot of a given
downlink superframe concerning the location of the next PRA slots.
If the PRA slots would have a constant location in each uplink
frame or superframe, the base station would not need to announce
their location in an Y slot, but it adds flexibility to the system
to reserve the base station subsystem the possibility of placing
the PRA slots in the most suitable way and to change their location
between superframes.
In one of the successive PRA slots the mobile station transmits,
according to arrow 21, a PRA message where it identifies itself and
informs what type of connection is requested (realtime, coding,
slot type etc. factors). Because there is no coordination
whatsoever between different mobile stations, it may happen that
several mobile stations transmit a PRA message simultaneously. In
that case one at the most is received. However, in FIG. 4a it is
assumed that the PRA message according to arrow 21 is received, in
which case in the PAG (packet access grant) slot of the next
downlink frame the base station notifies, according to arrow 22,
that a given uplink slot or slots are granted for the mobile
station. At the same time it informs the location of the granted
slot (slots) in the uplink superframe. In the packet access
protocols of the prior art the requesting station generally obtains
as its radio resource that time slot or other corresponding
resource point where it transmitted a successful capacity request.
According to the present invention, the slot (or slots) allocated
to the connection can be located anywhere within the scope of the
next uplink superframes.
When the mobile station has received information of the granted
radio resources, it starts data transmission according to arrow 23.
During the connection there may arise a situation where the mobile
station wants to increase the amount of radio resources it has
available. In that case it reserves further slots according to
arrow 24, by means of the same procedure that was explained above,
i.e. by transmitting a capacity request where it indicates what
size and type the new slot should be. It may also happen that
during the connection, the data transmission demand of the mobile
station decreases, and it wishes to reduce the employed radio
resources. Now it ends transmission in given slots according to
arrow 25, in which case the base station can allocate the released
slots to the use of other connections. Arrow 26 represents a
message whereby the mobile station ends transmission.
FIG. 4b serves to clarify the relation of some the above-mentioned
messages to the frame and superframe timing. Here we assume that
there are two frames 14 in each superframe 19. We further assume
that the downlink (DL) direction transmission occurs simultaneously
with the corresponding uplink (UL) direction transmnission, the two
being separated from each other through for example Frequency
Division Duplexing (FDD), i.e. placing them on different frequency
bands. Still further, we assume that in the middle of each frame 14
there is a range of control slots that appear shaded in FIG. 4b. It
is advantageous to place the control slot ranges coincidentally in
time in both downlink and uplink directions, because it will
prevent the loss of important control information due to
simultaneous traffic transmission. Taken the other way around, it
will also prevent the loss of any traffic transmission
opportunities due to control information reading. The chronological
order of the frames in FIG. 4b is from left to right.
The mobile station listens to the downlink transmission DL and
finds the slot addresses of the next available PRA slots in a
message that the base station transmits in a Y slot. These
available PRA slots are situated in the second frame of the
leftmost superframe in FIG. 4b. The dashed line represents a
logical connection between the slots, in other words it shows that
in the Figure the message sent in a certain Y slot governs the use
of the PRA slots in the following complete UL frame. The mobile
station uses a PRA slot to transmit a PRA message to the base
station. Taken that the attempt is successful, the base station
transmits a PAG message in a PAG slot of the next complete DL
frame. The PAG message tells the mobile station to use a certain
slot (or certain slots) RT from the next complete UL frame for the
desired transmission carrying real time traffic. The dashed lines
from the PAG slot to the next complete UL frame show that the
granted UL slot may be anywhere in the frame. The transmission
continues in the same slot until the data source is exhausted or
the base stations sends a separate RT uplink channel update command
(not shown in FIG. 4b).
A downlink realtime data transmission takes place according to
FIGS. 5a and 5b. A separate slot capacity request is not needed,
because the base station subsystem itself maintains the reservation
table for the slots and is thus able to direct downlink data
transmission to a suitable slot. The message that tells the
location of the chosen slot(s) to the mobile station can be
transmitted to the mobile station through packet paging (PP)
channels, at least one of which is read by each active mobile
station. The repetition of the PP message in the packet paging
channel, illustrated by arrows 27 and 2. means that the base
station transmits a PP message until the mobile station answers (or
until a given time limit is surpassed). The mobile station that has
received the transmitted PP message echoes, according to arrow 29,
the PP message back to the base station as a packet paging
acknowledgement (PPA). The base station starts transmission 30
after receiving, intermediated by the PPA, confirmation that the
call was received. The resource demands of downlink data
transmission can also change during the connection, in which case
the base station subsystem allocates more slots to the connection
(when resource demand grows) 31 or releases part of the slots (when
resource demand decreases) 32. Notification of the changes is
transmitted to the mobile station advantageously through packet
paging. Arrow 33 illustrates the ending of the transmission.
FIG. 5b clarifies the relation of PP and PPA messages and downlink
realtime data transmissions to the frame and superframe timing in
an embodiment where we again assume simultaneous FDD uplink and
downlink transmission with two frames 14 per superframe 19. After
the base station has transmitted a PP message, the first
acknowledging chance for the mobile station is in the PPA slots of
the next complete UL frame. After receiving the PPA acknowledgement
message the base station may start the realtime DL data
transmission in the next complete DL frame. It continues the
realtime DL data transmission in the same slot in each following DL
superframe, until the data source becomes exhausted (exhaustion not
illustrated in the Figure), which the mobile station detects when
it finds that the slot is empty.
Several simultaneous connections requiring realtime service may
exist, in between a given mobile station and base station, both in
the uplink aid downlink direction. Simultaneous connections are
also called parallel connections. According to a preferred
embodiment, the mobile station has a given temporary logic
identifier which distinguishes it among other mobile stations
communicating with the same base station subsystem. The length of
this identifier can be for instance 12 bits. In order to
distinguish between parallel connections, there may be used a short
(for instance 2-bit) additional identifier. When the mobile station
wishes, during a given connection, to start a parallel realtime
connection, it sends the base station subsystem a capacity request
where it notifies its temporary logic identifier as well as its
additional identifier with a value different than the value of the
additional identifier describing the preceding ongoing realtime
connection. Respectively, the base station subsystem may start a
new downlink parallel, realtime connection by transmitting a PP
message where it includes the logic identifier of the mobile
station for which the message is intended, plus an additional
identifier with a value different than the values of additional
identifiers describing already ongoing realtime connections. On the
basis of the additional identifier, each receiving station knows
whether the transmitting station wishes to increase the capacity of
some ongoing realtime connection or to start a new parallel
connection.
FIGS. 6a and 6b illustrate a non-realtime uplink data transmission
in a normal case. Arrow 34 corresponds to arrow 20 in FIG. 4a, i.e.
it represents the data concerning the location of the next PRA
slots transmitted in the Y slot of a given downlink superframe. In
one of the successive PRA slots, the mobile station transmits,
according to arrow 35, a PRA message where it identifies itself and
notifies how much non-realtime data it wishes to transmit. The
amount of data can be given for instance in bytes. In the next PAG
slot, the base station notifies, according to arrow 36, what is the
location of the control slot reserved as the uplink-direction
control channel in the downlink superframe. In the next control
slot, the base station transmits, according to arrow 37, the
locations in the uplink superframe of the first slots reserved for
the connection. In these slots, the mobile station transmits uplink
data according to arrow 38. The uplink slots are grouped for
instance so that 16 slots form a group. A control message according
to arrow 37 has transmitted for the mobile station information of
the location of these 16 slots. When the mobile station has
transmitted 16 slotted messages, it receives, according to arrow
39, in the next control slot from the base station subsystem a
response, where the base station informs how the data was received
in the slots of the first group. If the base station has found
fault in some slots, the mobile station must retransmit the data
contained in these slots. The control message illustrated by arrow
39 also contains information of the location of the slots belonging
to the next group, in which case uplink transmission continues in
these slots according to arrow 40. Transmission ends when the
mobile station has transmitted all of the desired information.
In the above cases, the realtime service of FIG. 4a, and in the
non-realtime service of FIG. 6a, the interpretation of the
reservation message is different. In the realtime service, there is
reserved a given radio resource (slot) for continuous use from
consecutive superframes. This means the same as the reservation of
a given transmission rate (x bits/s) for the use of the connection.
In the case of a non-realtime service, the resources are reserved
for the transmission of a given amount of bits or bytes, in which
case the data transmission rate need not be constant. If there are
a lot of radio resources available, the base station subsystem may,
in the control messages represented by arrows 37 and 39, grant for
the mobile station slots that are very near to each other. If the
rest of the traffic load of the base station is heavy, or if it
grows during the non-realtime connection, each superframe contains
less free slots, and the control messages described by arrows 37
and 39 grant for the mobile station slots that are located further
away from each other in the data flow.
FIG. 6b illustrates the timing in the setup phase of a non-realtime
uplink connection. The graphical conventions are the same as in
FIGS. 4b and 5b. The operation begins when the mobile station finds
the slot address of the next available PRA slot(s) in a message
that was transmitted in a Y slot from the base station. The mobile
station sends a PRA message, which is here supposed to reach the
base station at the first attempt. In the next complete downlink
frame containing PAG slot(s) the base station sends a PAG message
that identifies an NRT control slot (NC) from the following
superframe. In the first NC slot the base station transmits a
message in which it gives an address for a downlink ARQ slot as
well as the addresses for the first granted uplink NRT traffic
slots. The first one(s) of the granted uplink NRT Traffic slots may
be in the next complete uplink frame at earliest. The mobile
station starts transmission in the allocated NRT traffic slots and
the base station acknowledges the transmissions with ARQ messages
and grants further uplink NRT traffic slots in the following NC
slots. This continues until the total amount of uplink NRT data has
been sent.
A downlink non-realtime data transmission differs from what was
explained above and is illustrated in FIGS. 7a and 7b. When the
base station subsystem wishes to transmit non-realtime data for the
mobile station, it first transmits, according to arrow 41, a PP
message containing information of the location of the slot or slots
reserved to an uplink acknowledgement channel in uplink
superframes, as well as of the location of the first slots reserved
for the data to be transmitted in the downlink superframes. Arrow
42 illustrates the retransmission of the same PP message. When the
mobile station notifies in a PPA message according to arrow 43 that
it is ready for reception, the base station subsystem transmits the
data in the previously informed slots according to arrow 44. The
mobile station sends a positive or negative ARQ response 45 of the
received data, which response may also contain measuring results
used for downlink power regulation or similar information. If the
location or amount of the downlink slots is changed, the base
station subsystem notifies the mobile station to that effect,
according to arrow 46. The transmission ends when the base station
subsystem has transmitted all of the desired data and received a
positive response. Naturally the transmission may end prematurely,
if interference cuts the connection or the mobile station moves to
an area covered by some other base station.
In FIG. 7b the downlink non-realtime transmission starts with a PP
message sent by the base station in a PP slot of a certain downlink
frame. The mobile station responds by sending, in a PPA slot
identified in the PP message, a PPA message and optionally an empty
ARQ message in the corresponding slot that was also identified in
the PP message. The first downlink transmission will occur at
earliest in the next complete downlink frame following the frame
during which the base station received the mobile station's PPA
message. The mobile station acknowledges the downlink NRT
transmission in its ARQ replies and the process continues until the
non-realtime downlink data source has been exhausted (not shown in
the Figure).
In non-realtime connections there can be applied the same principle
of parallel connections that was explained above, in the
description of realtime services. However, because the radio
resource control method according to the invention aims at a
situation where up to all otherwise free slots can be temporarily
allocated to a given non-realtime connection, the concept of
parallel connections is not as important for non-realtime services
as it is for realtime services. In the case of non-realtime
services, a non-realtime data transmission task can generally be
finished before starting the next.
The invention does not require that the radio transmission
capacities in uplink and downlink transmission should be equal as
suggested by the graplucal layout of FIGS. 4b, 5b, 6b and 7b. On
the contrary, the invention allows the base station subsystem (or a
corresponding arrangement responsible for the division of radio
resources) to allocate slots from the uplink frames for downlink
traffic or vice versa For example in teleshopping, electronic
newspaper services and WWW (World Wide Web) browsing the need for
downlink capacity is far greater that the need for uplink capacity,
which could result in unbalanced resource usage if the system
capacities in uplink and downlink could not be made asymmetrical
dynamically.
When the slot allocation routine has decided to allocate an uplink
slot to downlink traffic the base station subsystem simply tells
the mobile station in a PP message that the slot it should receive
is in uplink domain (for example, on uplink frequency) instead of
the usual downlink. In the opposite situation, in which a downlink
slot is allocated for uplink transmission, a PAG message (in
realtime services) or an NC message (in non-realtime services) from
the base station subsystem allows the mobile station to use a
certain nominally downlink slot or slots for its uplink
transmission. It has to be noted, however, that changing the
transmission direction in the middle of a superframe requires a
guard interval in between, the length of which is equal to two
times the maximum propagation delay in the cell. It is therefore
advisable to group the slots into compact blocks that contain only
slots in one and the same transmission direction, in order not to
waste time in multiple consecutive transmission direction changes.
If the coverage area of a certain base station is so small that the
length of the guard interval is negligible, this restriction may be
somewhat relieved.
FIG. 8 illustrates the exchange of transmissions on the downlink
frequency band DL and uplink frequency band UL when some uplink
transmission capacity is reserved for realtime downlink use. The
graphical conventions are the same as in FIGS. 4b, 5b, 6b and 7b,
except that an additional crossed hatch now denotes a portion of
the frames received for downlink use and an inclined hatch denotes
a portion of the frames received for uplink use. During the first
superframe period the base station transmits in a Y slot Y1 a
message that tells the mobile station the location of PRA slots
PRA1 in the next complete uplink frame. The mobile station uses the
PRA opportunity to transmit a PRA message that reaches the base
station and results in a PAG message PAG1 in the next complete
downlink frame. The PAG message allocates a slot T1UL (or a group
of slots) to the mobile station. From that moment on until the
exhaustion of the uplink realtime data source (not shown in the
Figure) the mobile station uses this allocation regularly in each
superframe to transmit its realtime data.
In the second frame of the second superframe the base station
transmits a PP message PP2 indicating its willingness to transmit
realtime downlink data to the mobile station. The PP message PP2
identifies a slot (or a group of slots) T2DL from the second frame
in each following uplink superframe. The mobile station transmits
its PPA answer PPA2 in the next complete uplink frame, after which
the base station starts using the identified (cross-hatched)
portion T2DL of the uplink superframes for a downlink realtime
transmission. The uplink frequency band UL is now effectively
time-division duplexed (TDD). When the downlink transmission using
the slot T2DL ends (not shown in the Figure), the uplink frequency
band may return to a purely uplink state or the base station
subsystem may allocate uplink capacity to another downlink
transmission. Naturally there may be a multitude of simultaneous
uplink and downlink connections in use, in the setup phase, or in
the teardown phase, but for graphical clarity these are not shown
in the Figures.
Next we shall consider some further duplexing aspects. One
alternative is to arrange the uplink and downlink transmission in
each cell according to time division duplex (TDD). In that case the
transmission is not chronologically continuous in either of the
directions, but transmissions in the two directions alternate on a
frame basis during each superframe. Only one frequency band, common
for both the uplink and downlink directions, is needed in the cell.
If the users use a radio connection controlled according to the
method of the present invention for browsing the www (World Wide
Web) or for another similar purpose, where the data transmission
need in one direction is manifold compared to the other direction
(in www-browsing the volume of the downlink data transmission is
7-15 times the volume of the uplink data transmission), the time
division duplex can be arranged so that in each superframe, X
consecutive downlink frames are followed by Y consecutive uplink
frames (or Y consecutive uplink frames are followed by X
consecutive downlink frames), where the relation of the integrals X
and Y is X>Y. Still further, the cross-allocation scheme
explained previously may be introduced so that even if there is a
predetermined (fixed or dynamically changing) number of frames for
each transmission direction, the base station subsystem may
allocate downlink slots for uplink transmissions or vice versa.
FIG. 9 illustrates the exchange of transmissions in fully
time-division duplexed operation with all four possible
combinations of uplink, downlink, realtime and non-realtime. Each
row in the Figure represents a single frequency band that is used
(here: symmetrically) for both uplink and downlink transmission. A
superframe 19 consists of two frames 14, the first of which is for
downlink (DL) and the second is uplink (UL). The shaded portion of
each frame contains control slots. On the top row (Uplink RT) the
mobile stations finds in a Y slot downlink transmission the slot
addresses of the next available PRA slots, which are in the uplink
frame of the same superframe. It transmits a PRA message and
receives in the next downlink frame a PAG message allocating a slot
from the uplink frame. Thereafter the mobile station uses this
regularly occurring slot for uplink realtime transmission. On the
second row (Downlink RT) the base station transmits a PP message
that identifies a downlink information slot from the next complete
downlink frame on. The mobile station responds with a PPA message,
whereafter the downlink realtime transmission commences.
On the third row (Uplink NRT) of FIG. 9, the mobile station
transmits a PRA message after having found a correct PRA slot
address in a received Y slot message. In the downlink frame of the
next superframe the base station sends a PAG message that
identifies an NRT control slot (NC) from the downlink frame of the
third superframe. In the first NC slot the base station then
transmits a message in which it gives an address for a downlink ARQ
slot as well as the addresses for the first granted uplink NRT
traffic slots. The first one(s) of the granted uplink NRT traffic
slots may be in the uplink frame of the same superframe at
earliest. The mobile station starts transmission in the allocated
NRT traffic slots and the base station acknowledges the
transmissions with ARQ messages and grants further uplink NRT
traffic slots in the following NC slots. On the last row (Downlink
NRT) the downlink non-realtime transmission starts with a PP
message sent by the base station in a PP slot. The mobile station
responds by sending, in a PPA slot identified in the PP message, a
PPA message and optionally an empty ARQ message in the
corresponding slot that was also identified in the PP message. The
first downlink transmission will occur at earliest in the downlink
frame of the next superframe. The mobile station acknowledges the
downlink NRT transmission in its ARQ replies and the process
continues until the non-realtime downlink data source has been
exhausted (not shown in the Figure).
The radio resources control method according to the invention also
offers a possibility for regulating the transmission power during
radio connection. Above we referred to the fact that the control
slots contained in the superframes form one or several logic
control channels. One two-way logic channel per connection can be
called a SCCH channel (system control channel), which in a
preferred embodiment of the invention comprises, per each active
connection, one slot (in the above given time-frequency space
example one 200 kHz slot) per sixteen superframes both in the
uplink and downlink directions. The SCCH channel is used for the
whole duration of the active data transmission period, and it can
be employed for instance for transmitting measurements relating to
the power level, for arranging the mutual timing of the base
station subsystem and the mobile station, for transmitting
information relating to a handover to a different base station and
for transmitting commands directed from the base station subsystem
to the mobile station. The base station subsystem may for instance
command the mobile station into a so-called sleep mode, where the
mobile station is inactive for a predetermined period of time in
order to save power.
Another possibility offered by the method according to the
invention for regulating the power level of mobile stations is a
public power control channel (PPCC) independent of the slot
division in the frames. In order to realise it, each downlink frame
comprises a given PPCC slot containing a given amount of power
control bits per each possible slot in the corresponding uplink
frame. The amount of power control bits in the PPCC slot can be
chosen so that if the respective frame would be altogether composed
of the smallest possible slots, each slot would have its own bits.
When the frame in practice contains larger slots, too, in the
controlling of each larger slot there are used all those bits of
the PPCC slot that refer to the area of the larger slot. This
arrangement is illustrated in FIG. 10. The PPCC slot 47 comprises
the first power control bits 48 and the second power control bits
49. If the corresponding uplink frame 50 would comprise only small
slots 51 and 52, the first power control bits 48 would control the
first slot 51 and the second power control bits 49 would control
the second slot 52. If the small slots in the uplink frame are
modularly replaced by a larger slot 53, the power control bits 48
and 49 control the same slot 53, which brings either more
resolution or redundance to the control. Thus the structure of the
PPCC slot can be independent of the slot structure of the frames in
the uplink channel. A similar control channel structure and
principle can also be applied in other types of radio resource
control connected to the superframe. For example, the point of time
of the transmission of each slot can be controlled by a similar
procedure.
The slot allocation principles that were presented previously may
be applied also to the existing TDMA systems like the GSM system or
the IS-136 system to increase the data transmission capacity of a
given radio connection. The size of an allocated slot in a single
frequency band will come bigger in the chronological direction if
several consecutive slots of each cyclically repeated frame are
given to a single connection. Alternatively or additionally the
connection may get slots from both uplink and downlink frames,
without the limitation that uplink frame slots should be for uplink
use only and downlink frame slots for downlink use only. This means
that the newly allocated larger slot would actually consist of at
least two separate areas in the time-frequency space, with a
forbidden separator frequency band separating the nominal "uplink"
and "downlink" frequencies in a manner known as such from prior
art.
In the specification above, we have described a method for
controlling radio resources with reference to a few preferred
embodiments. It is obvious for a man skilled in the art that the
explained examples are not meant to be restrictive, but the
invention can, according to ordinary professional skills, be
modified within the scope of the appended patent claims.
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